Inorganic pigment



19, 1952 c. A. KUMINS INORGANIC PIGMENT Filed May 26, 1949 O 5 O 5 O G 5 5 4 4 Patented Aug. 19, 1952 corporation of Ohio application May 26; 1949, siiai No; 95,4l6 '1 ,4 Claims. (c l. 106-301) ish- "yellow, the color being dependent upon the. method of reacting the intermediates used in...10"

their preparation, temperature of calcination,..- and the-presence or absence of' "coprecipitated ziinc sulfidefl or [barium ,"s'ulfata among {other things, the zinc-sulfide giving a lightengreenershade, the barium sulfate giving an orange shade pigment.- Cadmium sulfide pigments as usually produced have good hiding'power, tinting strength, light resistance, heat'wresistance; and

resistance to alkalies and acids; W'hile they are v expensive, still they havebeen used in lithographic and color-printingbecause' they have the physical properties' justenumerated. The two main factors influencingthe'hiding power or opacity of a pigment are'(l) particle size; and (2) difference in index of refraction between vehicle and pigment. While it was known that thehiding power or opacity of;.cad.-.. mium sulfide, pigments could bevaried to a limited extent by varying particle size, the refractive index range of cadmium"sulfideipiments;being 2.506 to 2.529, relatively unchangeable', led to" the belief that cadmium sulfide pigments are inherently high hiding or opaque pigments. It is not surprising .therefore that the art is -.devoid of anyreferene' tocompletely, ad; 5-

mium sulfide pigments. I

I have discovered'-'thattransparent, brilliant golden, yellow cadmium, sulfide pigments; 103111398 prepared by controlling" the particlesizeof.the'.

cadmium sulfide within the range of OQQI @1095" 40;

micron, the average particle size being 0.02 micron This is accomplished by:

'1. Employing dilute solutions of reactants. 2. Reacting at relatively low"temperature's.

3. Rapid precipitation with vigorous agitation:

. 4. Rapid separation Lof -the precipitated cad-. miumsulfide from the mother liquor.

5; Eliminating the. calcination process which causescrystal growth.

In :order to prepare transp arent cadmium;sul'- Profitable" commercial practice. Theni'a'ximurrtliimixtlu're aver aJB-roIY inIi mill. Whenparticles Charles A. Kumins;Tuckahoe,"NfY assignor to Interchemical Corporation; New York, N. a

1 n'i'iinrsulfide[concentration of approximately 1110? cadmium, Salt.

allowalc lep'concentration before a diminution transparency occursv is 2.3 molesflper liter ofeithfer; reactant, cadmiumsaltor sulfidao'r a final cad-' insiper lit'er.; l, I" prefer. o; aqueous sol f trons of [cadmium salts varying between" .9 molar to ,2 .3-molar, plus 5%..exces's sulfide to sure completereaction' with the more ex ,A'gain, t' mpemtu ati. pitatioii is, kept relatively "'16s, to p'r'omo'tesmall particle size formation. Above C., larger particle size formation is promoted, so; that. transparency begi sto. diminish. mhexmwe temperature 11m n, is fth'e'ffreezirig point .orjjtjh reaction, medium? My'pre'fe'rred temperaturera'ngeis'10 90 C I Ra'pi precipit' tion' an Ivi'gorous. agitat on also contributetoflthe formation of fine particle size transparent 'CdSl Thecadmium.salt solutionjsQ added. to the alkali sulfide solution v or vice versa.

in a matterofiseveral minuteslduring .agitation sufiicient to give or approach turbulent flow-or,

the reaction medium, precipitated particle's'being kept in motion until'filtration.

P sle. s r@wth: is al a e t .-b-:. 1 the precipitated CdS from' the re:

.Earrin'iplel I' v r I To'-2 gals. 'o'f a-"0;195 molar solution of CdSOi' was added *with high-speed stirring-1.05 gals." 0.39-molarzsolution. of NazSBHzO, the reactionmedium being at 10 C. After precipitation'was' completed, the stirringwas continued for 1 minute, the slurry was filtered, and subjected to a pressure of about 5,900 p". s' i-"in lapi ess: to reduce the moisture content 'of the pulp *fioir'i' 83%(30 65%, 1The pressed cake'was mixe'd'withan equalf weight (dry pigment basis) of -a linseed l'modi? {phth'alateoxidiiiig type fresifi and; a dough niji'xer by mixing therein for 30 minutes; esman amou t of residual" ture was; re' ed by' passing"tlfeCd's-'al ajc'ti am'e i m, as by filtering the, precipitate ample '1.

from the CdS pulp were examined under the electron microscope, the average particle size was found to be 0.02 micron, with no particles larger than 0.05 micron. This compares with an average particle size of 0.4 micron for a representative commercial cadmium sulfide pigment.

Two ga1s..o f ,0.197 molar CdClz.-2 HzO ,,at 10 C. was added to 1 gal. of 0.394 molar Na2S.9HzO at the same temperature with vigorous agitation over a minute period. Agitation of the CdS slurry was continued for an additional minute,

after which it was filtered, washed free of;sodi-.

um chloride, and flushed intocastoroi1,;using the method of Example 1. The physical properties of the pigment in the pulp were. similar to those of Example 1.

Example 3 Two gals. of 1.15 molar CdSQi at 25 C. wasv addedtol, gal, of 2.3 molar Na2S.9H2O of'the same temperaturexover an interval of several minutes. with intensive high-speed stirring.

Aiftenprecipitation was complete, the, stirring was; continued for an additional ,minute, the CdS" slur ry-thenbein filtered, washed free of sodium sulfate,'andflushed intothe alkyd vehicle ofExslightly hazy. and had less brilliance and transp'arency than theproducts of Examples 1 and 2. Example jA'solution of 56:7 1bs..NazSl9HzO in, water- (24 galszigat" 35, C. was reacted by' rapid addition tl'ieretoof, an. aqueous solution of 53.4 lbs: cdcliz /g flzo in 72 gals. of water of :thesame temperature with vigorous high-speed stirring. Agitation was continued for 1 minute after all the cadmium had been added, theprecipitated pigment'was then filtered, and flushed into an alkyd resin solution. Films therefrom dried to a brilliant transparent gold finish.

Example 5 Ari-aqueous solution of 534 grams CdClz'.2 /2H20 infls2 -liters of water at Cfwas added rapidly with vlgor'ousagitation to anaqueous solution of 568 grams NazS.9HzO in 6 liters of water at the same temperature. Thereafter agitation w'as continued for 1 minute, the slurry of CdS was filtered, andfthe pigment washed freeoffwater soluble' salts. The ultimate pigment particles" averaged 0.02 micron, within the transparent-- particle size range: The 35% solids pulp thereor' Wasstable at roomtemperature over a period of.

hre mo t Exampleo V V A cold solution of gals. Na2S.9I-I2O was made up to a 0.65 molar concentration, and to it was added: 50.-gals., of: a cold:0.325. molar solution of CdGlzZF/zHZQ; The remainder of. the procedure min-Example 1. was followed, andsimilarprod ucts wereobtained;

" 1 7 Example 7 'Two. hundred gals. of anaqueous 0.195 molarsolutionof CdSO was rapidly added to 100 gals..ofaqueous 0.39 molar solution, of NazS.9I-I2O,-. both solutions being heated to 80 C.

with vigorous agitation. .Oneminutethereafter;

thesIurrywas. filtered, washed free of sodium sulfate, and the 1.7% solids CdS pulp storedat. roomv temperature for three. -months.

then werelstFll -in the tra sparent particle size- Finishes prepared therefrom were The: particles. 1

i CdOl Na s) Temp.-

Sam 501m Ppm Addition Result Mal Mal "C'. 1 0.197 0.394 90 Rapid..." Hazy.

2 3.0 3.0 5 .do Opaque.

. 3.0. 3.0 90 o. More opaque u than 2. 2.3- ..-..1.'l5: 5 -.do Very hazy. 0.191 0.394 20 Dropwise Vil'y slight aze. 0.197 0.394 90 --.do Slight haze. 0.197 -'-0.-,394 20 Rapid-- Transparent.

.394 0.191 20 do Do.

'4 range of 0.01-0.05 micron, averaging 0.02 micron. Equivalent results were obtained when potassium sulfide was substituted for sodium.

Example 8 Cadmium sulfide pigment was made under the following reaction conditions:

1 Plus 10% excess cadmium chloride solution.

Rapid: addition is completed within several minutes. Y 1 e M m e- 1 A brilliant transparent golden enamel l-wa s made up asfollowsz V I i Jami Ingredient H. Tby

50% dispersion of pigmentwf' Example l in alkyd resin= disclosed inExample ,1"-.- Alkyd resin of Example l 60% alkyd resin -H lFlashNsptha Nizplathenate drier (0.0l% ,each: cobalt," .ea

' v Total...

The stirred-i.-together; until" uniform, thedrier heingadded-last.

, Exam e 10 A brilliant transparent golden roller coating finishwas. prepared as: follows:

,. MPercent 1 Ingredient Y I 20% disliersion oi'pigment of Example I in alkyd of Ex I 23.5- .ampe" c i V .50%,s o1utiori naleated .ester-gum-malested. linseed oil-1 v 75.5

bgdied l nseedoil-m varnglene-kerosen e(7 g3) j Dnenasin Example-8:.--..;....-

Total-Q"-.. ":0

hef 'i jwas. a dedite ie' uniierrufmixtu e I:

Instead,v of. flushing, my, pigments .as disclosed a x pl sfle i li ad e v h e -W Theingredients-were; stirred togetheruntilg' unithe cadmium sulfide is to be flushed directly to the reaction kettle upon completion of precipitation and reflux the whole mass until the vehicle has thoroughly wet the cadmium sulfide, decant the water, and remove traces of water by passing the pigment dispersion over a 3-roller ink mill.

Example 13 Another method of transferring my pigments to a hydrophobic vehicle is to mix the washed pulp with an equal weight of flushin vehicle, pouring the entire mass into a high-speed mixer, and flushing therein. A small amount of wetting agent may be added, but is not strictly necessary since my pigments are hydrophobic. Traces of water are removed by passing the pigment dispersion over a 3-roller ink mill.

Example 14 A 50% solution of transparent Utah-type coal resin in low-solvency petroleum solvent having a 5-95% boiling range of 245-259 C., and a kauributanol value of 26, was pigmented with 25% transparent cadmium sulfide pigment by flushing pigment pulp therein. An equivalent amount of commercial cadmium sulfide pigment was mixed into the same amount of the same resin vehicle, so that this standard and the abovementioned dispersion of transparent pigment could be evaluated for hiding power.

In evaluating for hiding power, test paper composed of alternate black and white areas is used. When a film containing a high hiding pigment is drawn over these test areas, the spectral curve should approach that of the pigment as the underlying layer becomes covered by the colorant. On the other hand, a transparent material will not obliterate the spectral characteristics of the underlying areas in the black region (absorption of all transmitted light), but will contribute its chromophoric individuality to the White area (reflection of all transmitted light).

The figure illustrates the spectral properties of the alternate white and black test areas, 0| and 02, the efiect on each of standard cadmium sulfide pigmented composition, l l and I2, and the effect on each of my transparent cadmium sulfide pigmented composition, 2| and 22. In each case a film thickness-of 0.004 inch was applied. It is apparent that the high-hiding or opaque standard composition spectral curves, II and I2, approach that of the pigment; whereas the spectral curves for my transparent composition, 2! and 22, even with films as thick as 0.004 inch,

show that the reflectance characteristics of the black test area, 02, have hardly been affected,

those of the white area, 0|, exhibiting the effect of the yellow colorant to the extent shown at 2|.

I claim:

1. Method of preparing a transparent cadmium sulfide pigment comprising rapidly reacting a solution of a water soluble cadmium salt not exceeding 2.3 molar concentration with a solution of a water soluble alkali sulfide not exceeding 2.3 molar concentration at temperature not exceeding C., separating the precipitated cadmium sulfide from the reaction medium and preventing the growth of pigmentary aggregates, by transferring the pigment particles to a hydrophobic vehicle.

2. Cadmium sulfide consisting essentially of particles having an average particle size of 0.02 micron and having no particles larger than 0.05 micron, such particles yielding transparent golden yellow films when used to pigment organic film-forming coating compositions and having a negligible opacity as measured by the reflectance characteristics of such a film applied over a standard black background, the percent reflectance of such pigmented film not exceeding 2% more than the reflectance of the uncovered standard black background throughout the visi-,

ble spectrum, prepared by the method of claim 1.

3. A cadmium sulfide pigment pulp having particles averaging 0.02 micron particle diameter, with no particles larger than 0.05 micron, such particles yielding transparent golden yellow films when used to pigment organic film-forming coating compositions and having a negligible opacity as measured bythe reflectance characteristics of such a film applied over 'a standard black background, the percent reflectance of such pigmented film not exceeding 2% more than the REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,662,999 Cabot Mar. 20, 1928 2,061,368 O'Brien Nov. 17, 1938 2,237,311 OBrien Apr. 13,1941 2,406,472

OTHER REFERENCES Outlines of Paint Technology, Heaton Griffin & Co., Ltd., London, 1947, pg. 17.

- Nerlinger Aug. 27, 1946 

1. METHOD OF PREPARING A TRANSPARENT CADMIUM SULFIDE PIGMENT COMPRISING RAPIDLY REACTING A SOLUTION OF A WATER SOLUBLE CADMIUM SALT NOT EXCEEDING 2.3 MOLAR CONCENTRATION WITH A SOLUTION OF A WATER SOLUBLE ALKALI SULFIDE NOT EXCEEDING 2.3 MOLAR CONCENTRATION AT TEMPERATURE NOT EXCEEDING 90* C., SEPARATING THE PRECIPITATED CADMIUM SULFIDE FROM THE REACTION MEDIUM AND PREVENTING THE GROWTH OF PIGMENTARY AGGREGATES, BY TRANSFERRING THE PIGMENT PARTICLES TO A HYDROPHOBIC VEHICLE. 